Ultraefficient Ultraviolet and Visible Light Sensing and Ohmic Contacts in High-Mobility InSe Nanoflake Photodetectors Fabricated by the Focused Ion Beam Technique

A photodetector using a two-dimensional (2D) low-direct band gap indium selenide (InSe) nanostructure fabricated by the focused ion beam (FIB) technique has been investigated. The FIB-fabricated InSe photodetectors with a low contact resistance exhibit record high responsivity and detectivity to the ultraviolet and visible lights. The optimal responsivity and detectivity up to 1.8 × 107 A W–1 and 1.1 × 1015 Jones, respectively, are much higher than those of the other 2D material-based photoconductors and phototransistors. Moreover, the inherent photoconductivity (PC) quantified by the value of normalized gain has also been discussed and compared. By excluding the contribution of artificial parameters, the InSe nanoflakes exhibit an ultrahigh normalized gain of 3.2 cm2 V–1, which is several orders of magnitude higher than those of MoS2, GaS, and other layer material nanostructures. A high electron mobility at room temperature reaching 450 cm2 V–1 s–1 has been confirmed to be one of the major causes of the ...